Physiologists have long recognized that the hypothalamus controls all the secretory functions of the adenohypophysis with the hypothalamus producing special polypeptides which trigger the secretion of each pituitary hormone. An inhibitory factor was earlier characterized in the form of somatostatin which inhibits the secretion of growth hormone(GH).
A corresponding hypothalamic releasing factor for pituitary GH was long sought after, and in 1982, a polypeptide was isolated from an extract from a human pancreatic tumor, purified, characterized, synthesized and tested which promotes the release of GH by the pituitary. The formula of this 40-residue peptide is as follows: H-Tyr-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys-Val-Leu-Gly-Gln-Leu-Ser- Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Met-Ser-Arg-Gln-Gln-Gly-Glu-Ser-Asn-Gln-Glu -Arg-Gly-Ala-OH. The peptide is hereinafter referred to as hpGRF (for human pancreatic tumor GH releasing factor). A 44-residue amidated version of this peptide was isolated from another tumor which included Arg-Ala-Arg-Leu-NH.sub.2 at the C-terminus.